Demand for secondary batteries as an energy source has been significantly increased as technology development and demand with respect to mobile devices have increased. Among these secondary batteries, lithium secondary batteries having high energy density, high voltage, long cycle life, and low self-discharging rate have been commercialized and widely used.
Also, a lithium cobalt-based oxide, which is easily synthesized and has an excellent electrochemical performance including life characteristics, has been mainly used as a positive electrode active material for a lithium secondary battery. As portable devices, such as a mobile phone and a tablet PC, become smaller and smaller, high capacity and high energy as well as miniaturization have been required for batteries applied thereto. In order to increase energy per unit volume of the battery, packing density of an active material may be increased or a voltage may be increased. Furthermore, in order to increase the packing density, it is desirable to use an active material with a large particle size. However, since the active material with a large particle size has a relatively low surface area, an active area in contact with an electrolyte solution is also narrow. Since the narrow active area acts negatively on kinetics, relatively low rate capability and initial capacity are obtained.